The present invention relates to a magnetron sputtering system suitable for fabrication of a semiconductor device, and a method of fabricating a semiconductor device using the system.
Recently, there is a requirement to lower resistance and increase operational speed of semiconductor devices. To meet such a requirement, a self-aligned silicide (SALICIDE) process for forming a low resistance silicide film on a gate and source/drain regions in self-alignment is being examined and practically used. In this technique, since Ti and TiN have been already used in the existing process, it is expected to use TiSi2 as a silicide material in terms of self-alignment.
The use of TiSi2 however, has a problem on a so-called fine-line dependent effect. That is, in the case where TiSi2 is formed on a fine interconnection, a sheet resistance gradually increases with a reduction in the line width of the interconnection. The fine-line dependent effect becomes significant for an interconnection having a line width of 1 xcexcm or less, and therefore, it will bring a large problem for the future devices with finer-line geometries.
On the other hand, a silicide such as CoSi2 or NiSi does not exhibit such a fine-line dependent effect, and therefore, it is being actively examined as a silicide material used for the salicide process.
However, since Co or Ni has been little used as a material for a semiconductor process, it is inconvenient in terms of matching with the existing process, and further, since such a material is a ferroelectric substance, a film of the material is difficult to be formed by, for example, a magnetron sputtering system generally used for film formation of Ti, Al or the like in the semiconductor process.
To generate a high density plasma for increasing a film formation rate, a related art magnetron sputtering system has a configuration shown in FIG. 5, in which magnets 2 are disposed on a back surface of a target 1 for allowing a magnetic flux generated by the magnets 2 to be in parallel to a front surface of the target 1 as accurately as possible. When a voltage is applied in such a state, electrons exhibit a cycloidal motion as shown in FIG. 6. Consequently, as compared with a two-pole type DC sputtering system with no magnet, the frequency of collision of the electrons with a discharge gas in the vicinity of the front surface of the target 1 is significantly increased, to thereby generate a high density plasma. In FIG. 5, reference numeral 3 indicates a wafer to be processed; 4 is a wafer holder; 5 is a shield; 6 is a target stage for fixing the target 1 and fixedly containing the magnets 2; 7 is a motor for rotating the magnets 2; and 8 is an AC power supply for operating the motor 7.
For the target 1 made from a ferroelectric substance as described above, however, as shown in FIG. 7, part of an external magnetic field A2 is canceled by a magnetic field A1 due to spontaneous magnetization, so that a surface magnetic field of the target 1 becomes weak. As a result, when compared with sputtering using a paramagnetic substance, the generated plasma becomes weaker, failing to achieve sufficient film formation.
On the other hand, there is known a magnetron sputtering system of a type in which the magnets 2 are rotated for improving uniformity of the film formed by the system. In such a system, however, there occur eddy currents on the surface of the target 1 due to rotation of the magnets 2 as shown in FIG. 8. The occurrence of such eddy currents create a magnetic field to weaken the surface magnetic field of the target 1. Accordingly, for the target 1 made from a ferroelectric substance, the plasma becomes weaker, failing to achieve sufficient film formation.
Such a phenomenon causes even for the target 1 made from Ti, Al, or the like different from the ferroelectric substance; however, in this case, since the surface magnetic field is not weakened as described above, it does not obstruct film formation. On the contrary, for the target made from a ferroelectric substance, the surface magnetic field is weakened as shown in FIG. 7, and thereby generation of plasma is also weakened. Consequently, generation of a magnetic field due to eddy currents largely obstructs film formation of a ferroelectric substance.
An object of the present invention is to provide a magnetron sputtering system enabling film formation of a ferroelectric substance by suppressing occurrence of a magnetic field due to eddy currents.
Another object of the present invention is to provide a method of fabricating a semiconductor device, enabling film formation of a silicide of a ferroelectric substance using the above magnetron sputtering system.
To achieve the first object, according to the present invention, there is provided a magnetron sputtering system including: a flat target; magnetic field applying means, provided in the vicinity of a back surface of the target, for applying a magnetic field to a front surface of the target; and magnetic field rotating means for rotating the magnetic field applying means so as to rotate the magnetic field applied to the front surface of the target; wherein the magnetic field rotating means is provided with rotational speed varying means for varying a rotational speed of the magnetic field applied by the magnetic field rotating means.
In this magnetron sputtering system, the rotational speed of a magnetic field applied by the magnetic field rotating means can be suitably set by the rotational speed varying means in such a manner as not to cause a large eddy current on the surface of the target. As a result, even in the case of using the target made from a ferroelectric substance, it is possible to suppress the magnetic field from being weakened due to occurrence of the eddy current, and hence to stably generate a high density plasma.
The magnetron sputtering system is thus allowed to uniformly form a film of a ferroelectric substance such as Co or Ni, and hence to easily realize film formation of a ferroelectric material by the magnetron sputtering system which has been not adopted by the related art fabrication process for a semiconductor device.
Further, in this magnetron sputtering system, the rotational speed of the magnetic field can be suitably set depending on the kind of the target material; consequently, for example, films of a paramagnetic substance and a ferroelectric substance are easily formed in sequence using the same cathode only by exchanging the targets made from these substances from each other and setting the rotational speed depending on the kind of the exchanged target material.
To achieve the second object, according to the present invention, there is provided a method of fabricating a semiconductor device, including the steps of: forming a film of a ferroelectric substance on a polysilicon gate formed on a silicon substrate and on source and drain regions formed on a surface layer portion of the silicon substrate by sputtering using the above magnetron sputtering system; and forming a silicide layer on surface layer portions of the polysilicon gate, source region and drain region by annealing the substrate.
According to this method of fabricating a semiconductor device, a film of a ferroelectric substance such as Co or Ni is formed on a polysilicon gate and on source and drain regions formed on a surface layer portion of a silicon substrate. As a result, it is possible to uniformly form the ferroelectric film to a sufficient thickness, and hence to form a uniform silicide layer by the subsequent annealing. The fabrication method is thus allowed to form a uniform silicide layer having a low resistance without the fine-line dependent effect, and hence to fabricate a high speed semiconductor device with a high reliability.